Vacuum tube current amplifier



Feb. 6, 1951 E. G. LINDER VACUUM TUBE CURRENT AMPLIFIER 2 Sheets-Sheet 1 Filed Dec. 18, 1948 INVENTOR der Ernes BY Z7 2 .47

f ATTORNEY Feb. 6, 1951 E. G. LlNDER VACUUM TUBE CURRENT AMPLIFIER 2 Sheets-Sheet 2 Filed D60. 18, 1948 INVENIOR Erngsl @Lznder M32212 ATTORNEY Patented Feb. 6, 1951 '1.

. UNITED STATE PATENT E VACUUM ru jl ggti amrtirmit V Ernest G. Linder, Princeton, N. 3., assignor to; Radio Corporation of America, 'a corporation of Delaware Application December 18, 1948, serial No. 66,113

24 Claims. (01.250-2'15) increasing the lengths of the paths of electrons emitted initially by a radioactive source, and secondary electrons emitted from bombarded electrode, beyond the mean free path for collisions with the molecules of medium. This increase in lengths of the electrons is accomplished 'by applying a magnetic field to the medium whereby the electrons are deflected in their paths and pass by or'are cut ofi from striking the collector electrode. This phenomenon is defined as trapping, that is the electrons are trapped in their movements within the medium as they are reflected successively by the outer electrode. The effect of this trapping is that the paths of the electrons are lengthened beyond the mean free path for collision with molecules of the medium .and ionization of the medium occurs, with attending large conduction currents.

Among the objects of the invention are to provide improved methods of and means for ampli fying electrical currents.

Another objective is to provide improved methods of and means for controlling secondary radiation of electron from bombarded elements in a current amplifier tube.

Another object is to provide improved methods of and means for lengthening the paths of free electrons within a, gas filled tube to effect increased ionization of the gas within the tube.

Other objectives will be apparent from the description of the invention as hereinafter set forth in detail and from the drawings made a part hereof, in which Figure 1 is a sketch in vertical cross-section of one form of a tube of the invention; Fig. la is a cross-sectional view of the device of Fig; 1 taken along the section line In Figure 6 is a schematic diagram of a modification of the tube of the invention in which. the collector electrode is positioned unsymmetrical lengthwise along the. axis of the tube anddisplaced axially the tube as to the source of elec- I trons; Figure? is a's'chematic diagram of a modila; Figure 2 is a sketch in vertical cross-section of another tube in the invention; Figure 3 is'an enlarged view'of a portion of the-tube of Figure 2 taken on line 33 of Figure 2; Figure 4 is a schematic diagram of thetube of the invention and the path of a freeelectron under the influence of a magnetic field, butwithout colli'sion of the electron with thegas molecules within the tube; Fi ure 518a schematic .diagramoi the means g'heavywire or light'rods 3.

taut by spring ti Axially of the tube 2, is mounte'd accelerator and collector cylinder 5, suitably minals for collector 5. midsection of'collector5 and opposite cathode l 40 'are holes 1.

fication or the tube of the invention in which the collector electrode is positioned eccentric to the axis of the tube;,Figure 8 is a schematic diagram in horizontal cross-section of the tube of the invention illustrating the method of and for establishing an electric potential reflection zone within the tube and the path of a free electron under the influence of a magnetic field, but Without collision of the electron with the molecules of the gas within the tube; Figure 9 is a schematic diagram of the tube of the invention and an associated control circuit wherein tube end plates are utilized; and Figure 10 is a schematic diagram in horizontal crosssection of a tube of the invention including a suppressor grid for secondary electrons.

, Similar reference characters are applied to similar elements throughout the drawings.

I phenomenon the invention is based.

In Figure 1, numeral I represents the cathode filamen'twhich is supported in the axis of the envelope of the evacuated tube 2 by sectionsof Cathode l is kept supported .by' braces 6 which act as electric ter- At approximately the In practice these holes are about 0.040 inch in diameter and, in the tube shown, are four in number. Axially of the tube 2 and spaced near the side walls of the envelope 2 is mounted the cylinder electrode 8, suitably supported by,

brace 9 and wires I0, the latter acting as the electric'terminals of electrode 8. The tube 2 is gas'filled and at pressure of 10* to 10- mm.

which is short relative to the length of the associated electrodes. Asexamples of such relative lengths, Figures 1 and 2 represent fullscalle sketches of two tubes embodying the invention. The ratios of the lengths of the filaments l to its associated electrodes 5 and 8 are 1:10 and 1:3, respectively.

Extending outside and lengthwise the tube 2 is solenoid l I, which is connected to a. source of direct current (not shown), by which is set up the magnetic field=H (arrow). Electrode 8 and collector 5 are made of some magnetic field permeable material such as aluminum or appropriate alloys of stainless steel.

In Figure 2 is disclosed a tub'e'-s'iinilar -tothat shown in Figure l, in which is mounted. on one side of the axis of the tubeand"'nearthe side walls thereof, the cathode filament I 'whichis' supported by sections of heavy wire 3 and kept taut by spring 4. The collector 5 is m'ade in a form of a rod and is mounted in the axis of tube 2. Near the mid-section of electrode "8, lengthwise along the axis of tube 2 and opposite "cathode I, is cutanopening l2, such"thatthe "electrons emitted'from cathode: I mayeriter'the "s'pa'ce'within the' electr'o'de 8. Between cathode! "and electrode 8 is mounteda grid l3, in "any con- "Vntional'way such as wires I4, which'also"a'ct electric leads and terminalfor'grid l'3. A inagnetic field H isimpressed upon the space within the tubein a conventional w'ayfsuch as "disclosed in Figure 1. In FigureBisshown'an f'enlarg'ed view, partially brokenawa'y of the opening in electrode 8, and its "associated grid I3 and cathode l y In "operation, and with reference to "Figures "2,4a11 d 9, 'electronsemitted from cathode l are accelerated through the grid'f3 and opening fl 2'toward center of the tube by a source of elecf'tricpotentiallfi connected toelectrode 8, col- *lector 5 and cathode I. "By adjusting thestrength of the magnetic field I-I, the"'electronsmay be 'fmade to be deflected and pass-by collector 5 and '-thereafter bombardelectrode 8,"as shownby the arrow l 6. Upon successiverefiections' from electrode-*8, the initial electrons from cathode I continuebn their paths'asirrdicated by arrow [6 :a'nd are thus trapped in the spacew'ithirf the tube *2. Upon bombardment of 'electrode""8by the 'ini-- anal electrons secondary electrons are emittedyas -'shownbyarrows I 1. These secondary electrons "are accelerated toward electrode 5,"but,"responding to the magnetic fleldH, they are deflected "an Iikewise'become trappedwithm the tube. "-As the pathsof the initiarand "secondary elec- -trons' are increased andexceed the meannee path'for collision with the molecules "of the "gas "within the tube, ionization by'eollisio'n occurs, "causing further ionization oftheg'a's. 'With the io'nizationof the medium, conduction currents flow" between collector 5' and cathoded. "Afloafd *resistance 8 is placed in 'thiscircuit'that these "currents may be made available for useful pur- P@s 'Ihei'iow of electrons from cathode 'I'inay be {controlled by potentialsapplied to"gridl3 'b'y"a transformer [9, the primarybf "which'is connected to the source 28 of 'the'currents to be 5 3- 3 duces d l t a ping, ;is.- greatlylincreasd,

"plified and the secondaryof 'whichisnonnccted 'to'grid l3 and catho'del. The e'lectrons'from cathode l and the secondary electronsmay be 'fconfined within the 'spacenppo'siteto'collector s'b end plates 2| whichfare kept at aisli ghtly negative potential by an"electricfsource22connected by the platesll andcathode l. Beingat "negative potential, the "plates repelele'ctron's' approaeiung them. "The "system may begrounaed as'at 23.

electrons bombard electrode 8 and are trapped.

within the space between accelerator and anode 8, causing secondary electrons to be emitted 'and "cumulativeionization of the gas and conduction currents as hereinbefore described. The

' resulting 'conducti'oncurrents are utilized in load "l8 "W'hichis connected between electrode 8 and electric source [5. "Ihe control of the conduction currents is as previously disclosed. Grid l3 and cathode l are connected to the secondary of transformer l9, the primary of which is supplied by the currents to be amplified, that is, from -s'ource m. one l3'ma-y bebia's by electric "source-2 4.

''It '-'is desirable in current amplifier systems that the devices operate-withas large *a-multipllcation factor as possible. "The multiplication "fat-ital" may beincreased' by -lengthenin'g the paths of the initial electrons as shown in F'igures'6, "7 and8 or electrically "as disclosed in'Figures"-8 and 10.

30 'As shown in Figure"6,-"col1ector5 is so 'shortend that it does not exten'd -toa position opposite the opening l2. Theaverage path from cathode to "collector 5 is thereby lengthened, as illustrated by arrow 2 3. The tight spirals in--arrow 28'representzde flections o'f' the electrons upon striking ea s -m'elecules.

k The average'length of thepaths of the initial "electronsai'eincreasedas-shown in-Figure' 7, by 'positioning collector 5 eccentric '-the axis or the tube. The initial electrons have less chance of reachingcollector- 5 when collector 5 is placed in the indicated position. A further method or i 'creasing' the' multiplication'factoris that shown -in Figure 9, previously described; that is/by' con- 'a'ining- -theelectrons-within a limited volume or the tu'be b'y'end' plates' kept at a slightly negative potential.

'Ilie discharge-in the'tubesdisclosed' herein is -of -the Townsend type and may bedefined'by the equation:

Where "zn output current "p'u't current --a;=separation= of P electrodes 1 'e'='Na'pier'ian logarithm I base.

I Here, a maybe considered-the number ofelec- "trons :formed, per centimeter-spar. electron ma .isthe number of electrons formed,.-per Vpositive ion. By use of the-magnetic field, which..pro-

whereas' e .is-.-particularly unaffected by lthe-mag- }-netic field since the heayy.-po'si tive ions continue "insiibstantially 'straight-..pa. ths. It :is-de'sirable to make i lar'ge and p small-since-this= reduces To the likelihood ofinstability which occurswhen tliedenominator ofi theequationis zero. or

ar-'fi If 5 equals" zero," the current equation-reduced not reach electrode 8, but will be reflected by :this potential zone.28.v

It has. been found. that secondary electron emission from electrode 8 may be suppressed by 'carbonizing the inner surfaceof electrode 8 or r by painting that surface with aquadag. orv other similar materials. .This suppression increases the efficiency of the tube for reasons heretofore disclosed.. I I

Another means of suppressingsecondary electrons is by the use of a suppressor grid electrode 29 as shown in Figure 10.

I claim as my invention:

. 1. A vacuum tube comprising an evacuated envelope and inside said envelope: a filament, acylindrical apertured :first electrode concentrically juxtaposed said filament, a second electrode in concentrically spaced relation to said first electrode, the said first electrode having said aperture immediately opposite said filament to form a restricted opening therethrough and a control -grid positioned betweensaid filament and said first electrode opposite said aperture.

2. A vacuum tube comprising an evacuated envelope and inside said'envelope: a filament disposed midway the length of said tubeand-juxtaposed said envelope, a cylindrical apertured first electrode juxtaposed said filament, a second electrode disposed adjacent to said first electrode, the said first electrode having said aperture immediately opposite said filament to form a restricted opening therethrough, and a control grid positioned between said filament and said first electrode opposite said aperture. a

3. A vacuum tube comprising an evacuated envelope and inside said envelope: 3, filament structure extending lengthwise the tube'that includes a mid-portion or filament wire and a plurality of conductingand supporting heavy wire end sections, a cylindrical apertured first electrode concentrically juxtaposed said filament, a second electrode in concentrically spaced relation to said first electrode, the firstelectrode having said aperture immediately opposite said filament wire to'form a restricted opening therethrough, and a control grid positioned between said filament and said first electrode opposite said aperture. 4. A vacuum tube comprising an evacuated enlvelope and inside said envelope: a filament struc- I ture extending lengthwise the tube that includes a mid-portion of filament wire, a plurality of conducting and supporting heavy wire end sections and a resilient section, whereby the said structure is kept taut, a cylindrical apertured first electrode concentrically juxtaposed said filament, a second electrode in concentrically spaced relation to said first electrode, the said first electrode having said aperture immediately opposite said filament to form a restricted opening therethrough, and a control grid positioned between said filament and said first electrode opposite said aperture.

5. A vacuum tube comprising an evacuated envelope and inside said envelope; a filament, a cylindrical apertured first electrode concentrically aperture in said first electrode comprising .a restricted opening therethrough and thesecond electrode being positioned in the axis of the tube, and a control grid positioned between saidfilament and said first electrode opposite said aperture. 6. A vacuum tube comprising an evacuated envelope and inside said envelope: a filament, an apertured cylindrical first electrode juxtaposed said filament, a second electrode disposed adjacent to said first electrode, the said aperture in said electrode being disposed immediately opposite said filament to form a restrictedopening therethrough and the second electrode being positioned eccentric the axis of the tube, and a control grid positioned between said filament and said first electrode opposite said aperture.

7. A vacuum tube comprising an evacuated envelope and inside said envelope: a filament, an apertured cylindrical first electrode juxtaposed said filament, and a second electrode disposed adjacent to said first electrode, the aperture in said first electrode being disposed to form a restricted opening therethrough, a control grid positioned between said filament and said first electrode opposite said aperture, and a second grid juxtaposed said first electrode.

8. Discharge tube apparatus for amplifying electric currents comprising: an envelope enclosing a source of initial electrons, electrode means for accelerating said electrons through a restricted area within the tube, further electrode means for accelerating said electrons through the medium of the tube, means for reflecting said further accelerated electrons successively within said medium, means for applying a magnetic field to said medium whereby said electrons are trapped within said medium and conduction currents are generated, electrode means for collecting-said conduction currents, and control electrode means for controlling the fiow of said initial electrons in accordance with the characteristics of the currents to be amplified. a

9. Discharge tube apparatus for amplifying electric currents comprising: an envelope enclosing a source of electrons, electrode means for accelerating said electrons through a restricted area within the tube for generating further electrons by cumulative gas ionization, further electrode vmeans for accelerating all of said electrons through the medium of the tube, means for refleeting said further accelerated electrons, means for accelerating said further accelerated electrons and secondary electrons within said medium, means for applying a magnetic field to said ine diurn whereby said further accelerated electrons and said secondary electrons are trapped within said medium and conduction currents are generated, means for collecting said conduction currents, means for and controlling the flow of said electrons in accordance with the characteristics of the currents to be amplified.

10. Discharge tube apparatus for amplifying electric currents comprising: an envelope enclosing a source of initial electrons, electrode means for accelerating said electrons through a restricted area within the tube, further electrode means for accelerating said electrons through the medium of the tube, means providing an equipotentiai zone in said envelope .for reflecting said further accelerated electrons, means for applying a magnetic field to said medium whereby said elec- :7 itrons are :trapped .within said medium and :con- *ducticncurrents are generated, meansiorcollecting said conduction currents, and means for controlling "the flow of said initial electrons in ac- ;cordance with the characteristics f the currents stoxbeamplified.

.111. Discharge tube apparatus for amplifying electric currents comprising: an envelope enclosing a source or" initial electrons, electrode means -foracceleratingrsaid electrons through a restrict- :ed .areaxwithin the tube, further electrode-means ifor saccelerating said electrons through the medium ;of the "tube, means for providing a negaitively charged potential zone in said 'tube for reflecting said :further accelerated electrons, :means. for applying a magnetic field to said me- -dium'whereby said electrons are trapped within saidmedium and conduction currents are genaxerated, means for collecting said conduction currents,.-and means; for controlling the flow of said withinsaid medium and conduction currents are generated, means for collecting said conduction ;-c urrents, and means ,for controlling the fiow of maid-initial electrons in accordancewiththev char- ;acteristics of the currents to be amplified.

:13. A discharge.tub.e current amplifiercompris- :ing: cathode'means for producing initial electrons within the said tube, electrodemeans for acceler- -.-ating said electrons through a restricted area within said tube, further electrode meansfor furvther accelerating said electrons within 'the medium of the tube, reflecting electrode :means .for reflecting said further accelerated elec- .trons,.means for trapping said further acceler- .,ated electrons, whereby conduction currentsa-re generated, .electrode means for ,coliecting said .currents and control electrode means for controlvJingthe flow of. said initial electrons inaccordance i-with the characteristics of the currents to .be -amplified.

1.4..An amplifier as defined in claim 13,-the electro-n producing means being concentrated :in a; space immediatelyadjacent said restriced area.

15. An-amplifier-as defined in claim 13, the said ,,electron producing means being in theaxis of said .tube and concentrated at the mid-section;thereof,

#8 ithe isaid accelerating means zbeing .a .cylindrlcal electrode surrounding said electron sproduoing means, and said res.tricted area 'being massage- -w-aysiinsaidrelectrode.

.216. An amplifier asdefinedinclaimzlli,the-Said electron producingvmeans areipositioned. adjacent the. envelope :oflsaid :tube and concentrated atathe mid-section lengthwise of .said tube :and :the: said further accelerating :means .being :an electr d positioned :in the axis .:of .said :tube and char ed gtO apositive potential.

17. An amplifier as defined innlaimil'zi, :thesaid further acceleratingmeans-.beingzan electrode in .the .axis of said tube and charged =.t0 a epositive potential, Tithe said electrode .being so :positioned axially thetube th-atnoportion thereof isrlaterally opposite said electron producingmeans.

118. Anamplifier-asdefinediin claimzhizthe said electron producing means being positioned adjacent the. envelopeofsaid ,tubeand the. said liurther accelerating ,means beingan electrode :positioned eccentric to the axis of the tube.

19. An amplifier as defined in claim:13,-the-sa1d reflecting means being a :secondary electron responsive surface.

v20. An a-mplifieras defined inclaim 13, thesaid reflecting means being .a surface charged rat a negative potential whereby 'the vsaid further :acceler jtedielectronsare repelledby.theelectricfield :atsaid surface.

21. An amplifier zasidefinedsin claim 1:3, rthearefleeting means-being a cylindrical electrode andra n a ive y ch g d grid jux aposed thereto, whereby thesaid furthenaccelerated' electlionszare repelled bythe electricfield of said-grid.

22. An amplifier according to claim '13,;inc1udns meansfor confin ng: the saidzfurther 252 215 ated electrons within'a restricted portion of said tube.

23. vAn amplifier as definedin claim 13,;the said reflecting surface being carbonized, -:wherel:qy secondary electron emission at said :surface ;;iS suppressed.

24. An amplifieras defined in claim .13, thesaid reflecting surtace being coated with equadae. ..whereby secondaryelectronemhsion at;.said surafaceis suppressed.

E NEST G. ;.LINDE,R.

:REEERENCES CITED The following references are -of:record='i-n*-the file of this patent:

UN TED iS'IYATIZESPATI'ENIS 

